The present invention relates to a rotary valve disposed between intake and exhaust air sources and suction and discharge units, to supply or stop supplying air.
In the sheet feeding unit of a sheet-fed offset printing press, a suction unit connected to an intake air source and a discharge unit connected to an exhaust air source are used to feed stacked sheets to the feeder board one by one. More specifically, in order to draw the highest sheet by suction with the suction unit, the air of the suction unit is taken by an intake pump serving as the intake air source. In order to blow air to the stacked sheets or to separate the top sheet drawing by the suction unit from the second top sheet underneath, or in order to discharge reverse air that facilitates separation of the sheet conveyed from the suction unit to the feeder board, exhaust air is supplied by an exhaust pump serving as the exhaust air source.
The ON/OFF timings of each of the intake air and exhaust air correspond to the rotation angle of the printing press main body. This series of timings are controlled by a rotary valve.
FIG. 9 shows a conventional rotary valve.
Referring to FIG. 9, in a rotary valve indicated by reference numeral 30, a main body 2 formed into a substantially rectangular parallelepiped shape is fixed to a frame 5 of a sheet feeding unit through a bracket 5a. The first and second suckers, a leveling foot, and an air blower (not shown) are provided to the sheet feeding unit. As shown in FIGS. 10A and 10B, the lower portion of the main body 2 in one end side in the direction of an arrow Z swells in an arcuated manner to constitute a swelling portion 2a.
A through hole 3 extending in the direction of an arrow X is formed in the swelling portion 2a, and a cylindrical sleeve 4 is fixed to the inner circumferential surface of the through hole 3. A valve body 6 is engaged in the sleeve 4. End shafts 6a and 6b on the two ends of the valve body 6 are rotatably supported by the sleeve 4 through bearings 7a and 7b. The valve body 6 rotates in an interlocked manner with rotation of the printing press through one end shaft 6a.
Four air passages 9a, 9b, 9c, and 9d, each having an open upper end and a lower end communicating with the through hole 3, are formed in the upper portion side of the main body 2 corresponding to the swelling portion 2a, to extend in the vertical direction (the direction of an arrow Z). Of the air passages 9a to 9d, the air passages 9a and 9b, on their upper end side, are connected to an intake pump (to be described later) through hoses 17a and 17b. The air passages 9a and 9b constitute an intake air passage. The air passages 9c and 9d, on their upper end side, are connected to an exhaust pump (to be described later) through hoses 17c and 17d. The air passages 9c and 9d constitute an exhaust air passage.
Air passages 10a, 10b, 10c, and 10d are formed in the main body 2 to extend in the direction of the arrow Y perpendicularly to the intake air passages 9a and 9b and the exhaust air passages 9c and 9d, respectively. One end of each of the air passages 10a to 10d opens to the outside of the main body 2 while the other end thereof communicates with the through hole 3.
Of the air passages 10a to 10d, the air passages 10a and 10b are connected to suction heads (to be described later), serving as the first and second suckers, through hoses 18a and 18b. The air passages 10a and 10b constitute a suction air passage. The air passages 10c and 10d are connected to nozzles (to be described later), respectively serving as a leveling foot and an air blower, through hoses 18c and 18d. The air passages 10c and 10d constitute a discharge air passage.
Reference numeral 31 denotes a reverse air passage for the suction heads. The reverse air passage 31 is formed between the suction air passages 10a and 10b to extend from the upper end of the main body 2 to the circumferential surface of the valve body 6 through the sleeve 4. The exhaust pump (described above) is connected to the upper opening end side of the reverse air passage 31 through a hose (not shown). At a certain machine angle of rotation of the valve body 6, the lower end of the reverse air passage 31 communicates with the suction air passages 10a and 10b through a notch (to be described later) formed in the valve body 6.
Vent holes 11a, 11b, 11c, and 11d are formed in the sleeve 4 to respectively correspond to the intake air passages 9a and 9b and the exhaust air passages 9c and 9d. Vent holes 12a, 12b, 12c, and 12d are also formed in the sleeve 4 to respectively correspond to the suction air passages 10a and 10b and the discharge air passages 10c and 10d.
As shown in FIG. 10A, a notch 13a through which the vent holes 11a and 12a communicate with each other is formed in the circumferential surface of the valve body 6 corresponding to the intake air passage 9a and the suction air passage 10a. Similarly, a notch 13b through which the vent holes 11b and 12b communicate with each other is formed in the circumferential surface of the valve body 6 corresponding to the intake air passage 9b and the suction air passage 10b, at a position displaced from the notch 13a in the axial direction and to be phase-shifted from the notch 13a in the rotating direction of the valve body 6.
As shown in FIG. 10B, a notch 13c through which the vent holes 11c and 12c communicate with each other is formed in the circumferential surface of the valve body 6 corresponding to the intake air passage 9c and the suction air passage 10c. Similarly, a notch 13d through which the vent holes 11d and 12d communicate with each other is formed in the circumferential surface of the valve body 6 corresponding to the intake air passage 9d and the suction air passage 10d, at a position displaced from the notch 13c in the axial direction and to be phase-shifted from the notch 13c in the rotating direction of the valve body 6.
In this arrangement, when the valve body 6 is rotated in an interlocked manner with rotation of the printing press main body, the notch 13d of the valve body 6 is in communication with the vent holes 11d and 12d of the sleeve 4, and the exhaust air passage 9d and the discharge air passage 10d communicate with each other through the notch 13d. Thus, air exhausted from the exhaust pump flows through the air passages 9d and 10d that communicate with each other through the notch 13d, and is discharged from the nozzles to blow air to the sheets.
When the valve body 6 is continuously rotated, the notch 13a is in communication with the vent holes 11a and 12a, and the intake air passage 9a and the suction air passage 10a communicate with each other through the notch 13a. Thus, as shown in FIG. 10A, intake air A taken by the intake pump flows through the air passages 9a and 10a that communicate with each other through the notch 13a, to draw the top sheet by suction with the first sucker.
When the valve body 6 is continuously rotated, the notch 13c is in communication with the vent holes 11c and 12c of the sleeve 4, and the exhaust air passage 9c and the discharge air passage 10c communicate with each other through the notch 13c. Thus, as shown in FIG. 10B, exhaust air B exhausted from the exhaust pump flows through the air passages 9c and 10c that communicate with each other through the notch 13c, and is discharged from the nozzle serving as the leveling foot. At this time, the discharged air is blown to a portion between the top sheet drawn by the suction heads and the second top sheet underneath, to separate them from each other.
When the valve body 6 is further rotated, the notch 13b opposes the vent holes 11b and 12b, and the intake air passage 9b and the suction air passage 10b communicate with each other through the notch 13b. Thus, the intake air taken by the intake pump flows through the air passages 9b and 10b that communicate with each other through the notch 13b, to draw a sheet by suction with the second sucker.
Simultaneously, the notch 13a is displaced from the vent hole 12a, and the intake air passage 9a and the suction air passage 10a are disconnected from each other. Thus, suction air supply is stopped, and the sheet suction operation with the first sucker is stopped.
Since a notch 32a of the valve body 6 is in communication with the reverse air passage 31, the reverse air passage 31 and the suction air passage 10a communicate with each other through the notch 32a. The exhaust air exhausted from the exhaust pump flows through the air passages 31 and 10a and is blown out of the first sucker, and the sheet is quickly released from the first sucker that has ended the suction operation. As a result, a sheet which is conveyed over the feeder board while being drawn by the second sucker will not be cut or bent.
When the second sucker during sheet conveyance is located above the feeder board, the notch 13b is displaced from the vent hole 12b in accordance with rotation of the valve body 6, and the intake air passage 9b and the suction air passage 10b are disconnected from each other. Thus, intake air supply is stopped, and the sheet suction operation with the second sucker is stopped. At this time, a notch 32b is in communication with the reverse air passage 31, and the reverse air passage 31 and the suction air passage 10b communicate with each other through the notch 32b. The exhaust air exhausted from the exhaust pump flows through the air passages 31 and 10b and is blown out of the second sucker. The sheet is quickly released from the second sucker that has ended the suction operation, and is supplied onto the feeder board.
In the discharge operation of the nozzles, if the air discharge time of the nozzles is shorter than the suction time of the suction heads, the notch 13c constituting the air passage from the exhaust pump is formed smaller along with the rotation of the valve body 6 than the notch 13a constituting the air passage from the intake pump, as shown in FIGS. 10A and 10B. Inversely, in the suction operation of the suction heads, if the suction time of the suction heads is shorter than the air discharge time of the nozzles, the notch 13a is formed smaller than the notch 13c, as shown in FIGS. 12A and 12B.
As shown in FIG. 10B, if the notch 13c is made small to shorten the air discharge time from the nozzles, along with rotation of the valve body 6, as the opening of the vent hole 11c is enlarged, the opening of the vent hole 12c is narrowed. For this reason, a predetermined air pressure cannot be obtained on the nozzle side.
Accordingly, the amount of air from the nozzles becomes short and air blowing to the stacked sheets is not performed sufficiently, and two or more sheets are undesirably drawn by the suction heads. In this case, operation of the printing press must be stopped, or the printing press may cause a trouble to decrease the productivity. Since the supply amount of reverse air from the suction heads becomes short to delay sheet release from the suction heads, the sheet may be cut or bent to degrade the printing quality.
When the operation speed of the printing press increases, the time of forming the air passage in the rotary valve is shortened. Then, a predetermined discharge air pressure from the nozzles cannot be obtained, in the same manner as described above.
Meanwhile, as shown in FIG. 12A, if the notch 13a is made small to shorten the suction time of the suction heads, along with rotation of the valve body 6, as the opening of the vent hole 11a is enlarged, the opening of the vent hole 12a is narrowed. As a result, a predetermined air pressure cannot be obtained with the suction heads, and defective sheet supply may occur.
FIG. 11 shows the relationship in pressure of the input/output air of the rotary valve of FIG. 10B during the discharge operation. Referring to FIG. 11, reference numeral b1 denotes the pressure of the exhaust air input to the rotary valve 30. The pressure b1 is the pressure of the exhaust air from the exhaust pump. Reference numeral b2 denotes the pressure of the discharge air output from the rotary valve. The pressure b2 is the pressure of the discharge air from the nozzles.
When the machine angle of rotation of the printing press becomes .beta.1, the notch 13c of the valve body 6 is in communication with the vent holes 11c and 12c of the sleeve 4, and discharge air is supplied from an exhaust pump 36 to the nozzles through the exhaust air passage 9c, the notch 13c, and the discharge air passage 10c. The pressure of air supplied to the nozzles at this time is expressed as a pressure P. Subsequently, when the machine angle of rotation becomes .beta.2, the notch 13c is displaced from the vent hole 12c, the vent hole 12c is closed with the circumferential surface of the valve body 6, and supply of the discharge air to the discharge air passage 10c is stopped.
At this time, in the conventional rotary valve 30, a pressure b3 of the discharge air between the machine angles .beta.1 and .beta.2 of rotation becomes lower than a necessary pressure b4 by a pressure difference .DELTA.P. This is due to the following reason. Since the notch 13c is small, along with rotation of the valve body 6, as the opening of the vent hole 11c is enlarged, the opening of the vent hole 12c is narrowed, so the air exhausted from the exhaust pump 36 is not sufficiently supplied to the nozzles.
FIG. 13 shows the relationship of the input/output air of the rotary valve shown in FIG. 12A during the suction operation. As shown in FIG. 13, even during the suction operation, a pressure loss in air of the rotary valve occurs. Reference numeral a1 denotes the pressure of the intake air input to the rotary valve 30. The pressure a1 is the pressure of intake air from the intake pump. Reference numeral a2 denotes the pressure of the suction air output from the rotary valve 30. The pressure a2 is the pressure of the suction air of the suction heads. As shown in FIG. 13, a pressure a3 of the suction air between the machine angles .beta.1 and .beta.2 of rotation becomes higher than a necessary pressure a4 by a pressure difference .DELTA.P.